1. Field of the Invention
This invention relates to improvements in a vehicular power plant, and more particularly to a joining structure of the power plant to join a plurality of housing members accomodating mechanisms of the power plant.
2. Description of the Prior Art
In an automotive vehicle, power output from an engine is, in general, transmitted to road wheels through a transmission upon being suitably changed in rotational speed thus to drive the road wheels. As shown in FIGS. 6A and 6B of the drawings, an internal combustion engine 1 is incorporated through a clutch or a torque converter with a transmission 2, thereby constituting a power plant 3. More specifically, during assembly of the power plant 3 using the torque converter, a torque converter casing (housing member) 4 is joined with a cylinder block 1a while a transmission housing (housing member) 2a is joined with the torque converter casing 4. Such joining between the cylinder block 1a and the torque converter casing 4 and between the torque converter casing 4 and the transmission housing 2a is accomplished by means of bolts disposed along the periphery of each housing member.
However, with the above conventional power plant joining structure, when the bolts are fastened, stress is unavoidably concentrated only at locations to which fastening force of the bolts are applied, so that initial compressive stress due to bolt fastening force cannot be developed at other locations than the above fastening force applied location. As a result, the contacting joining surfaces of the opposite housing members are unavoidably locally separate from each other under deformation of the power plant 3 due to exciting force of engine combustion power and inertial force of reciprocally moving members. This reduces the total local rigidities of the joining surfaces which largely affects the deformation of the power plant 3. As a result, the joining rigidity between the joined housing members are lowered. Accordingly, there is a tendency of generating resonance vibration of the power plant 3 in a low frequency range under the effect of a joining rigidity between the cylinder block 1a and the transmission housing 2a which rigidity serves as a main spring. This unavoidably increases noise during acceleration and booming noise inside the vehicle passenger compartment.